Most of the liquid soaps today are made by one of two basic methods. In the first method, molten neutral fats or oils comprising triglycerides are reacted with a neutralizing agent in either a batch or continuous process to form a soap, with glycerine being recovered as a by product. Batch processes which have been employed to manufacture soap by this method include the kettle or full boiled process, the semiboiled process, the cold process and the autoclave process; and continuous processes for practicing this method include the Sharples process and the Mon Savon process. However, all of these processes are characterized by neutralization of molten or liquid fats and oils.
In the second method, fatty acids obtained by splitting or hydrolysis of natural fats and oils are neutralized with a suitable neutralizing agent in either a batch or continuous process. Again, the fatty acid typically is employed in molten or liquid form. Use of molten fatty acids requires application of heat to melt the various fatty acids which, with the exception of oleic acid (m.p. of 14.degree. C.) and the coconut fatty acid mixture obtained from coconut oil (m.p. of 25.4.degree. C.), are solids at room temperature, i.e., 21.degree. C. to 25.degree. C. For example, the melting points of various C.sub.12 -C.sub.18 fatty acids follows: lauric acid-47.degree. C.; myristic acid-54.degree. C.; palmitic acid-62.degree. C.; stearic acid-69.degree. C.; and tallow fatty acid-40.degree.-45.degree. C.
Because the foregoing processes utilize significant amounts of energy, various proposals have been made to produce soap using reduced amounts of energy. For example, U.S. Pat. No. 1,722,687 discloses a process for manufacturing a dry soap powder comprising reacting an emulsion of 46% by weight of palm kernel fatty acids in water having a temperature of 50.degree. C. with a particulate soda ash in a pinned disc mill to form a soap powder. U.S. Pat. No. 2,730,539 discloses a process for the manufacture of soap without addition of external heat by reacting molten tallow at 100.degree. C. with a 50% sodium hydroxide solution in a Muller mixer for two and one half hours to produce a soap wherein saponification was completed overnight. U.S. Pat. No. 4,336,203 also discloses a process for producing soap wherein liquid fatty acid and 50% sodium hydroxide are reacted at 50.degree. C. in the high shear field of a rotor-stator machine to produce a soap having a moisture content of about 15% by weight. Similarly. U.S. Pat. No. 4,376,079 discloses a process for making a soap containing 20% to 50% moisture by reacting a dispersion of metal oxide or hydroxide with an emulsion of fatty acid in water. U.S. Pat. No. 2,578,366, too, discloses a process for making soap containing 19-25% by weight of water comprising mixing solid fatty acid crystals dispersed in a melt of liquid fatty acid with a sodium hydroxide solution at 54.degree. C. to 100.degree. C. However, the energy saving accomplished by the foregoing processes is based upon the elimination of the heat required for drying the resultant soap rather than by eliminating the heat required for melting the fatty acid.
Based upon the foregoing discussion, it is apparent that there is a need for a process of making liquid soap for use in the manufacture of cosmetic products, e.g., shaving cream, skin lotions, etc., wherein energy can be conserved by omitting the need for energy input to melt the fatty acids and, preferably, by omitting the need for use of external cooling to reduce the temperature of either the soap or the ultimate cosmetic product.